The goal of this proposal is to identify an appropriate animal model for use in studying the effects of long-term noise on the inner ear of humans. Specifically, it is proposed to investigate the amount of temporary threshold shift (TTS), its growth and decay in squirrel monkeys and humans to long term exposure to noise. In addition, histopathological data will be collected from the monkeys. A variety of noises will be used. These noises will be artifically generated noises and recorded factory noises. Experimental exposure durations will replicate work-day durations. By combining the human testing facilities of one institution, the animal testing facilities of another, and the histological facilities of a third, a complete systematic investigation of the appropriateness of the squirrel monkey as an animal model for use in studying the effects of long-term noise on the inner ear of humans can be accomplished. Once the relationship between man and monkey is established, the monkey can be used and the appropriate stimuli can be systematically extended into durations and levels considered dangerous to humans. The behavioral and histological consequences of long term exposure to noise can then be evaluated and generalized to man.